An electronic device is sometimes mounted to a substrate using an array of interconnection balls. The interconnection balls are usually formed of tin lead solder.
One such electronic device is a ball grid array (BGA) package. A BGA package typically includes a substrate having an upper side and a lower side. An integrated circuit is mounted on the upper side of the substrate. Encapsulant covers the integrated circuit chip and the upper side of the substrate. Bond wires electrically connect the integrated circuit to the substrate. Solder interconnection balls are fused to the second side of the substrate. The BGA package is mounted on a printed circuit board (PCB) or other substrate by reflowing the interconnection balls so that the interconnection balls become fused to metallizations of the PCB, thereby forming an electrical connection between the BGA package and the PCB.
Another type of electronic device that uses interconnection balls is known as a xe2x80x9cflip chipxe2x80x9d. A flip chip is an integrated circuit having bond pads on a side thereof. Solder interconnection balls are electrically connected to the bond pads. The flip chip is mounted on a PCB by fusing the interconnection balls to metallizations of the PCB, thereby forming an electrical connection between the flip chip and the PCB. An insulative adhesive underfill material is provided beneath the flip chip to help secure the flip chip to the PCB.
With both the BGA package and the flip chip, the physical and electrical connection to the PCB is accomplished by heating and reflowing the interconnection balls. Such a soldered connection is time consuming and expensive to make, and difficult to take apart. Flip chips also require underfill, which adds to manufacturing time and cost.
The present invention includes an apparatus for mounting an electronic device that has an array of interconnection balls (e.g., a BGA package or a flip chip) or other electrically conductive contacts (e.g., a leadless chip carrier package) on a substrate such as a PCB. Neither soldering nor underfill is required.
One embodiment of a socket within the present invention includes a hollow rectangular frame and one or more cantilever beams extending from the frame. The socket is located on and fixed to the substrate (e.g., a PCB). The electronic device is inserted into the socket past the cantilever beams. The cantilever beams apply a continuous downward pressure on the top of the electronic device. This pressure presses the interconnection balls or other contacts on the opposite lower side of the electronic device against corresponding metal pads on the substrate, thereby forming an electrical connection without soldering between the electronic device and the substrate.
Another embodiment of a socket within the present invention includes a body having cantilever beams extending from one side thereof. The body may be a hollow frame or a solid plate. The electronic device is seated in the socket against the body and within the beams. The socket is attached to the substrate by inserting the cantilever beams into corresponding apertures of the substrate. The beams pull the body toward the substrate. Since the electronic device is between the body and the substrate, the body in turn presses the electronic device and its interconnection balls against the substrate. The continuous downward force exerted on the device by the socket ensures a reliable electrical connection between the electronic device and the substrate without soldering.
Further features and advantages of the invention will appear from the detailed description given below and the accompanying drawings.